Signaling system



Dec. 26, 1950 w. L. SHAFER SIGNALING SYSTEM Filed April 25. 1947 lNl ENTOR By WL. SHAFER ATTORNEY Patented Dec. 26, 1950 SIGNALING SYSTEM William Leroy Shafer, Mount Lebanon, Pa., as-

signor to American Telephone and Telegraph Company, a corporation of New York Application April 25, 1947, Serial No. 743,900

3 Claims. (01. 179-16) This invention relates to signaling systems and particularly to systems in which selective signals are transmitted by the opening and closing of a signaling circuit.

Qbjects of the invention are a modification of dialing circuits to prevent the transmission of a false impulse at the end of the train created by the impulse contacts of a dial, and in general the improvement of dial impulse transmission where a holding bridge is provided in the dial circuit of an operators position.

In dialing circuits, such for instance as are provided at manual switchboards for transmitting trains of dial impulses corresponding to the digits of a called subscriber's number, it is usual to provide a supervisory bridge comprising a retardation coil which is connected across the line. over which the dial impulses are to be transmitted, as long as the dial is in normal position. Nhen the dial is moved ofi normal, it is usual to short-circuit the retardation coil so that the cur- :rent in the line will increase rapidly each time the im ulse contacts of the dial are closed to terminate a dial impulse, thereby to insure the reoperation of the impulse receiving relay which is being controlled by the dial impulses. At the end of each train of impulses, the retardation coil is reconnect d across the'line; and, due to the increase in the inductance in the loop circuit over the line, there is a momentary reduction in the current which tends to, and frequently does, cause the release of the impulse receiving relay, thereby causing an incorrect switching operation or an incorrect registration of the called subscribers number. The probability of causing a false release of this impulse receiving relay when the retardation coil is thus reconnected in the impulse transmitting circuit. is somewhat reduced by connecting a non-inductive resistor in parallel with the retardation coil at the time that the retardation coil is first reinserted in the impulse transmitting circuit and thereafter opening the path through the resistor. Such an arrangement is disclosed in W. B. Strickler Patent 1,747 849, granted February 18, 1930. H0wever, this method of preventing false switching or registration due to reinsertion of the retardation coil in the impulsetransmitting circuit-is not fully efiective.

This invention is a dialing circuit arrangement in which a retardation coil or other inductive winding connected in series with the impulse contacts of the dial across a line over which dial impulses are to be transmitted, and in which very large capacitance is connected in parallel with the inductive winding from the time the dial is moved oil-normal until a short interval of time has elapsed after the dial reaches normal.

A feature of the invention is a large capacitative shunt connected across an inductive winding in series with the dial impulse contacts during the transmission of a train of dial impulses to e ifect a desirable shaping of the dial impulses. Another feature of the invention is a large capacitative shunt connected across an inductive winding which is in series with the dial impulse contacts to stabilize the current level in the impulse circuit at the end of a train of dial impulses and thereby prevent a false release of the impulse receiving relay.

A clear and complete understanding of th invention and its features will be facilitated by the following description of a system embodying the invention as illustrated schematically in the drawing which consists of a single figure. The invention is not limited in its application to the system and specific arrangement shown in the drawing but is generally applicable to systems inwhich trains of impulses are created by a set ofimpulse contacts and transmitted in a signaling circuit to control the operation of selective switches or registers.

. The system disclosed in the drawing includes .a branch exchange and a dial central oflice. The branchtexchange comprises the subscribers stations "land 60 and lines I! and 6!, :a cord circuit CI for use in establishing connections between lines and trunks in the branch ofiice, an operators position including a dial circuit and telephone set common to a plurality of cords at a. position of the switchboard in the branch office, and an outgoing trunk circuit 10. The central office is represented by an impulse receiving relayBl and a subscribers station 90. .The relay 8| may be the line relay of :a first selector to which the trunk from the branch exchange is extended responsive to seizure of the trunk in the branch ofiice; or relay 8i may be the impulse receiving relay of a register which .is associated with the trunk responsive to seizure in the branch ofiice.

The subscriber stations I0 and 6B are of the usualtype provided in manual, common battery oflices. The line circuit'associated with line H includes a, line relay l3 which is operated when the receiver is removed at the station Ill to initiate a call. The operation of relay I3 lights the answering lamp M to indicate a call is awaiting i 'ill l i pil-x Whenthe operator inserts plug 15 of a cord Cl into jack 32 to answer the call, relay i3 is released and lamp it thereby extinguished. Relay is is operated by the current in the line loop, prev nting the lighting of the rear cord supervisory lamp ill; but the front cord supervisory lamp 2? is lighted. With the talking key 25 of cord Cl operated, a conversational connection is established between the calling station ill and the operators telephone set. If the call is to another station in the branch exchange, plug 38 is inserted in a jack 52 associated with a called line it; and ringing key 2% is actuated to transmit ringing current from generator RG over the called line to signal the called station. Sleeve relay remains normal since the sleeve of jack 62 is connected to ground; and the supervisory lamp 2? remains lighted until the call is answered. When the call is answered, relay 23 operates and lamp 2? is extinguished. Supervisory relay [8 remains operated as long plug i is in jack l2 and the receiver is on the hook at station it. Talking battery is connected to both stations through the windings of retard coil 22. When the calling and called subscribers replace the receivers, supervisory relays i8 33 release and lamps l9 and 2'5 are lighted; whereupon the cord is disconnected irom the calling and called subscribers jacks.

Assume now that the call initiated at station I1] is a call to the station til in the central ofiice. In this case the line H is extended through jack l2 and plug id of cord CI to the operator set and through plug 333 and jack l2 to an outgoing trunk circuit iii which terminates at the central office. Relay 2% is operated in a circuit which includes the sleeve conductors of plug 33 and jack l2, thereby to open the battery feed through the retard coil 22, to short-circuit the winding of supervisory relay 23, to extinguish supervisory lamp 2? and to cause the operation of relay H. The ring-up relay M is disconnected from the trunk when the plug as is in jack l2; and, as soon as the impulse receiving relay all in the central office is connected to the 'runk and with key 25 of cord Cl operated, a loop circuit is completed for operating relay 8!. This circuit is traced from battery through the left winding of relay 3 l, lower conductor of the trunk to the branch exchange, a contact of jack l2 and ring conductors of jack l2 and plug a contact of ringing key I a back contact of night and through dialing key a front contact of relay 2%, a front contact of talking and dialing key 2%, conductor 32, retardation coil impulse contacts SI of dial 5U, conductor 35, contacts of keys 28 and 2S, tip conductors of plug and jack l2, upper conductor or" the trunl: to the central ofiice and through the right winding of relay 8! to ground.

Each time a digit of the called subscribers numher is dialed, the off-normal contacts 52 of the dial 5:! are actuated thereby closing a circuit for operatively energizing the lower winding of relay 5%. Relay disconnects the ring-side of the operators telephone et from the cord circuit C! and closes a cir uit for operating relay 53. Relay 53 disconnects the ring-side of the operators telephone set in n the repeating coil 57, closes a circuit for ener -g the upper winding of relay 5t, closes a circuit for operating relay 59 and connects condenser E" '11 parallel with the winding of retardation coil mentioned loop circuit for he transmission of dial impulses to relay 8!. Relay 5Q disconnects the tip and ring of the rear plug ifi'from the tip and ring of the front plug 36 and connects the thereby preparing the aforetip and ring or" the rear cord to the right windings of repeating coil 52 and the windings of relay 58. Relay operates in series with the calling line loop 1 relay is held operated as long as relay remains operated. When released, the dial returns to norn a1 and the impulse contacts 5| open and close the iinpulsing circuit as many t' es as there are units in the digit dialed. Relay 8i rele ses and reoperates each time the impulsing circuit is opened and closed to effect a corresponding switching operation or digit registration. When the dial reaches normal, relays 53 and release in that order, both of these relays being slow in releasing. Relay 58 and 5? remain operated under control of the talking and dialing key 2 until thi key is released.

When dialing is completed and the talking and dialing 23 is released, relays 58 and 55} release. Relay ll remains operated in a locking circuit through its idner upper front contact to ground at a back co ltact of key 2 Talking battery is furnished to the calling station ill from the central office. W hen the calling subscriber at station i=3 replaces the rec iver at the end of conversation, relay eleases thereby lighting the supervisory lamp is and closing a circuit for operating Belay 2i splits the cord to prevent the station 53 in case the trunk ii! is seized oiiice before the cord Cl is disconnected jacks and l2. When the plugs are withdrawn, relays 2?, 2i and 2 release and lamp 2 is extinguished.

Heretofore it has been usual to connect a resistor in parallel with retardation coil as when relay 54 operates and then to short-circuit both the resistor and coil when relay operates, thereby to reduce the inductance and resistance of the inipulsing circuit to insure the reoperation of the impulse receiving relay between successive impulses of a digit; and in such an arrang ment, the short-circuit across the resistor and coil 55 is opened when relay :38 releases and the resistor shunt across the coil is opened when relay releases thereby minimizing the effect of introducing the coil 55 into the iinpuleing cirsuit so as to reduce the probability of a false release of the impulse receiving relay at the end of a train of dial impulses. This heretofore employed arrangement was not wholly enective to prevent release of the impulse receiving relay; and, in the arrangement embodying invention shown in the drawing, a condenser 56 of high capacity, for instance 86 inicrofarads, is connected in parallel with coil 55 when relay 53 operates in place of shcrt-circuiting coil 55 as in the prior art arrangement. Condenser charges as soon as it is connected in parallel with coil as; and when the dial is released at the end of the dial wind-up, the first opening of the dial impulse contacts causes the release of relay 3| and while the pulsing circuit is open, condenser discharges through coil When the pulsing circuit is reclosed by the impulse contacts of the dial, condenser 5% again charges and the current through thwindings of relay 3i builds up fast to cause the fast reoperation of relay 8| the inductive efiect of coil being neutralized due to the fact that the large capacitance of condenser constitutes a very low impedance shunt across the coil Since any rounding of the build-up of the circuit is due solely to the inductance of relay cl and the capacitance between the line conductors, the shape of the pulse is substantially the same as in prior arrangemerits which short-circuit the retard coil during the transmission of dial pulses. However, since the retardation coil resistance is included in the pulsing circuit, the maximum current through the winding of relay 8! between pulses is not as large as is the case if the coil 55 were short-circuited; consequently relay 9i releases faster when the pulsing circuit is opened by the dial than would be the case if coil 55 were short-circuited. Thus a pulse shaping is attained which efiects fast release of relay 3! each time the pulsing circuit is opened, and fast operation of relay 8! when the pulsing circuit is reclosed. When the impulse contacts or" the dial reclose the pulsing circuit at the end of the last pulse of a train, condenser 56 charges and the current in the pulsing circuit builds up the same as at the end of the prior pulses of the train. By the time that relay 53 releases and opens the shunt through condenser 55, the condenser will be substantially fully charged and current through coil 55 etabilized; and consequently any momentary drop in the current through the winding of relay 8!, when the shunt is opened, will be insufiicient to cause release of relay 8 l. a

What is claimed is:

1. In combination, a circuit including in series a current source, an impulse receiving relay, an inductance and impulse contacts for opening and closing said circuit to transmit impulses to said relay, a capacitance, and means for connecting said capacitance in parallel with said inductance during the transmission of impulses to said relay, said capacitance being large to insure the response of said relay to each impulse of said train and to prevent the false release of said relay when the parallel path through said capacitance is opened at the end of a train of impulses.

2, In combination, a dial impulse sender having impulse contacts and oil-normal contacts, a retardation coil connected in series with said impulse contacts, a condenser having a large capacitance, means comprising a slow-to-release relay controlled by said off-normal contacts for connecting said condenser in parallel with said retardation coil while said dial is off normal.

3. In combination, an impulse receiving relay, a dial impulse sender having off-normal contacts and impulse contacts, said impulse contacts connected in a series circuit including a winding of said relay and a source of direct current and being actuated when any digit is dialed to interrupt said circuit during the return movement of said dial as many times as there are units in the digit dialed, a retardation coil connected in said circuit in series with said impulse contacts, a condenser, a relay controlled by the oil-normal contacts of the dial, said relay having normally open contacts for connecting said condenser in parallel with said retardation coil, the capacity of said condenser being large and said relay being slow to release whereby sufiicient time elapses after the last impulse of a train is transmitted to said impulse relay for the current in said circuit to have reached a substantially steady state before the parallel path through said condenser is opened.

WILLIAM LEROY SHAFER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,664,665 Currier et a1. Apr. 3, 1928 1,747,849 Strickler Feb. 18, 1930 1,864,381 Trechcinski June 21, 1932 1,901,628 Brainard Mar. 14, 1933 1,997,205 Van Mierlo et a1. Apr. 9, 1935 2,218,659 Saville Oct. 22, 1940 

